Peristaltic pump

ABSTRACT

IN A PERISTALTIC PUMP WHEREIN SPACED IMPELLER ROLLERS ON A ROTOR SUCCESSIVELY TRAVERSE A SECTION OF RESILIENTLY FLEXIBLE TUBING, THE IMPELLER ROLLERS ARE SHAPED TO FLATTEN A CENTRAL LONGITUDINAL PORTION OF THE TUBING AND TO PERMIT THE OPPOSITE LONGITUDINAL EDGES OF THE FLATTENED TUBING TO BULGE TO AVOID EXCESSIVE STRESSING OF THE TUBING.

March 2, 1971 PERISTALTI C PUMP Filed Feb. 1o, 1969 United States PatentO 3,567,345 PERISTALTIC PUMP John W. Ballentine, Manhattan Beach,Calif., assignor to W. S. Shamban & Co., West Los Angeles, Calif. FiledFeb. 10, 1969, Ser. No. 798,086 Int. Cl. F 04h 43/00, 43/08 U.S. Cl.417-477 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTIONThe invention relates to a peristaltic pump of the type disclosed in theBallentine et al. Pat. 3,402,673, which disclosure is herebyincorporated into the present disclosure by reference.

In the operation of such a peristaltic pump, successive impeller rollerson a motor-driven rotor traverse a section of resiliently flexibleplastic tubing to squeeze the tubing across its width to seal theinterior of the tubing at successive traveling points and thereby formsuccessive pump chambers which iirst expand longitudinally while open attheir output ends. To squeeze or flatten the tubing, the impellerrollers may press the tubing against a cooperating arcuate wall of thepump or, instead, the section of the tubing may be anchored at itsopposite ends against longitudinal slippage to cause the tubing to forma sling and the impeller rollers may flatten the tubing by placing thesling under tension.

A rotor equipped with three impeller rollers severely stresses thetubing at a relatively high frequency that is three times the r.p.m. ofthe rotor to cause the structure of the tubing to deteriorate at arelatively rapid rate. The consequent short service life of the tubingis expensive in the cost of replacement as well as in the time lost forreplacement and in the labor cost involved.

The broad object of the invention is to improved such a peristaltic pumpin a manner to substantially increase the service life of the tubing forcorresponding reduction in this expense.

SUMMARY OF THE INVENTION It is well known that the number of cycles ofstress that a plastic member can withstand before it fails increases asthe severity of the stress is reduced and that the rate of increase isexponential. Thus if a given stress just suicient to cause immediatefailure of the plastic is reduced to 75%, the plastic will survive a fewcycles; if the stress is reduced 50%, the plastic will survive over onethousand cycles; reduction of the stress from 50% to 40% increases thenumber of cycles to a hundred thousand and below 40% the curve attensout to such an extent that when the stress is reduced to approximately25% the service life of the plastic is increased indefinitely.Heretofore it has been regarded as impossible to take advantage of thisfact because of the logical assumption that failure to flatten theplastic tubing to the usual drastic degree would cause the efficiency ofthe pump to drop otf in the same exponential manner and in additionwould eliminate the self-priming capability of the pump.

Repeated testing of the life of a whole series of plastic tubes inperistaltic pumps reveals that the tubing fails at the two oppositelongitudinal side edges of the attened tubing where the tubing wall isfolded to a sharp ICC band. The present invention is based on thediscovery that the degree to which the tubing is flattened in these twocritical zones can be reduced substantially without significantsacrilice of the pump el'liciency. Accordingly, the invention teachesflattening the tubing by the impeller rollers to the usual degree onlyalong a wide central longitudinal zone of the tubing, each of the twolongitudinal edge portions of the flattened tubing being permitted tobulge to permit the 180 folds to assume a liberal radii of curvature.

An important advantage of carrying out this concept is that thereduction in the stressing of the tubing wall greatly lessens thegeneration of heat in the tubing material, which reduction in heat initself not only conserves the tubing but also reduces the possibility ofthe flattened walls of the tubing being welded together under thepressure of the impelled rollers. The lessening of the likelihood ofwelding the two walls together makes it possible to flatten the centrallongitudinal zone of the tubing to greater than the usual degree.

In one embodiment of the invention, each of the impeller rollers isimproved by providing the roller with two circumferential grooves thatare spaced yapart to register with the two longitudinal edge portionsrespectively of the flattened tube. The two grooves are of a dimensionand of a cross-sectional curvature to permit the two longitudinal edgesof the flattened tubing to bulge to a radius of curvature to reduce thestressing of the material to the desired degree without significantlysacrificing the efciency of the pump. The two circumferential grooves ofan impeller roller serve the further purpose of tracking the tubing inthat the two grooves cooperate with the budged edge portions to tend tomaintain the tubing in alignment with the impeller roller.

In a second embodiment of the invention, each of the impeller rollers isonly wide enough to flatten the desired central longitudinal zone of thetubing, the relatively narrow width of the roller permitting the twolongitudinal ledges of the flattened tube to bulge to the desireddegree. In this second embodiment of the invention, the trackingfunction may be carried out by providing the relatively narrow impellerroller with hub extensions on its opposite ends and by mounting disks onthe two hub portions respectively to confine the tubing in alignmentWith the impeller rollers.

The various features and advantages of the invention may be understoodfrom the following detailed description and the accompanying drawings:

BRIEF IDESCRIPTION OF THE DRAWINGS In the drawings, which are to beregarded as merely illustrative:

FIG. 1 is a perspective view of the peristaltic pump incorporating thepresently preferred embodiment of the invention;

FIG. 2 is a view of an impeller roller of the pump shown in FIG. l, theview being partly in section and partly in side elevation and showinghow the impeller roller permits bulging of the opposite longitudinaledges of the flattened tubing;

FIG. 3 is a similar sectional view of a second embodiment of an impellerroller; and

FIG. 4 is a graph showing how the service life of a plastic member isincreased by reducing the degree to which the member is cyclicallystressed.

DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION FIG. 1 shows aperistaltic pump mounted on a base plate 10 wherein a motor 12 providedwith reduction gearing in a gear case 14 drives a rotor 15 that isprovided with three impeller rollers 16 on three corresponding spindles18. The three impeller rollers 16 successively traverse a section oftubing 20 adjacent a concentrically curved wall 22 of the pump structurethat terminates in two outwardly turned wings 24. The tubing 20 isanchored against longitudinal slippage by two corresponding clamp plates2S that straddle the tubing and clamp the tubing against the two wings24 respectively. For adjustment each of the two clamp plates 25 isformed with a longitudinal slot 20 that receives a corresponding fixedscrew 28, the screw carrying a suitable thumb nut 30.

The arrangement may be such that the impeller rollers 16 successivelyflatten the tubing 20 by pressing the tubing against the arcuate wall22. If desired, however, the tubing may be formed into a sling betweenthe two clamp plates 25 with the sling dimensioned relative to the orbitof the impeller rollers to be placed under tension by each roller inturn to such degree as to flatten the tubing to the desired extent.

In accord with the teaching of the invention, each of the impellerrollers 16 is so shaped and dimensioned as to flatten only the majorportion of the width of the tubing along a central longitudinal zone ofthe tubing and to permit the two longitudinal edges of the flattenedtubing to bulge to the desired degree. For this purpose each of theimpeller rollers in the pump of FIG. 1 is formed with twocircumferential grooves 32 near its opposite ends as best shown in FIG.2, the two grooves being dimensioned and spaced to register with the twolongitudinal edges of the flattened tube and to permit the longitudinaledges of the flattened tube to bulge as indicated at 314. In IFIG. 2 theimpeller roller 16 compresses the tubing 20 against the surface of thearcuate wall 22 but, as heretofore stated, the impeller roller need notcooperate with the arcuate wall in this manner.

The main body portion 35 of the impeller roller 16 that is bounded bythe two circumferential grooves 32 is of uniform diameter but tapers atits opposite ends into the two grooves. The main body portion 35 isnarrow enough to permit the bulging of the opposite longitudinal edgesof the tubing and with the two circumferential grooves 32 registeringwith the bulged edge portions 34 of the flattened tubing, the twocircumferential grooves tend to track the tubing in the sense ofconfining the opposite longitudinal edges of the flattened tubing andthus tend to maintain the tubing in alignment with the impeller roller.

`Because the opposite longitudinal edge portions of the flattened tubingare permitted to bulge in the manner described, small voids 36 areformed by the small radii of curvature inside each of the two 180 foldsof the tubing wall at the opposite longitudinal edges of the fiattenedtubing but, surprisingly, these voids do not cause the efficiency of thepump to drop to a significant extent. In any event, the degree to whichthe life of the tubing is extended is of importance far exceeding theimportance of any loss in efficiency of the pump if the impeller rollersare appropriately shaped and dimensioned within the expected skill inthis art.

The graph shown in FIG. 4 is taken from Fundamentals of Plastics byRichardson and Wilson. The graph shows how, as previously explained, thelife of the plastic member increases exponentially as the relativestress of the plastic member is progressively reduced. In continuoushighly accelerated tests carried out twentyfour hours a day, sections ofplastic tubing acted upon by conventional impeller rollers to create apump discharge at 13 p.s.i. were found to survive approximately oneweek. Substitution of impeller rollers of the new configurationdisclosed herein resulted in extending the life of the tubing to thirtydays. In practice the service life of a section of tubing is increasedat least three fold.

FIG. 3 shows a second embodiment of an impeller roller, designated 16a,wherein the full width of the roller is substantially the same as thewidth of the body portion 35 of the rst described impeller roller. Theimpeller 4 roller 16a is of uniform diameter but is tapered with roundededges at its opposite ends to permit the opposite longitudinal edgeportions of the flattened tubing to bulge with the desired curvature.

For the purpose of tracking the flattened plastic tubing, each impellerroller 16a is provided with hubs 40 at its opposite ends on which aremounted corresponding disks or flanges 42 that overhang the oppositelongitudinal edges of the flattened tubing to confine the flattenedtubing and thus maintain the flattened tubing in correct alignment withthe impeller roller. It is to be noted that the hubs 40 provide adequateclearance for bulging of the opposite edge portions of the flattenedtubing. The disks 42 may be fixed relative to the impeller roller 16a ormay be free to rotate to minimize relative movement between the disksand the edges of the flattened tubing.

My description in specific detail of the selected embodiments of theinvention will suggest to those skilled in the art various changes,substitutions and other departures from my disclosure.

What is claimed is:

1. In a peristaltic pump wherein impeller rollers on a rotorsuccessively traverse a section of resiliently flexible tubing in acompressive manner to cause fluid in the tubing to travel lengthwise ofthe tubing, the improvement comprising:

each of said impeller rollers being of an axial dimension substantiallyless than the width of the tubing when the tubing is fully flattened,each of said rollers 'being positioned centrally of the width of theflattened tubing to flatten a central longitudinal portion of the tubingwith the opposite longitudinal edge portions of the flattened tubingfree to bulge to avoid damaging stressing of the opposite longitudinaledge portions;

each of said impeller rollers being provided with hubs at each of itsopposite ends of substantially smaller diameter than the roller to clearthe opposite bulged edge portions of the tubing; and

two disks rigidly mounted on the respective hubs to block sidewisemovement of the tubing out of alignment with the roller and to maintainthe tubing in alignment with the roller.

2. In a peristaltic pump, the combination of:

fixed structure having an arcuate concave surface;

a section of resiliently flexible tubing extending along said arcuateconcave surface,

the width of said concave surface exceeding the width of the tubing whenthe tubing is flattened; and

a rotor within the region defined by said concave surface;

a plurality of rotary means journalled on said rotor and movable therebyadjacent said concave surface to flatten the tubing against the concavesurface,

each of said rotary means having a central cylindrical portion ofuniform diameter of less width than the width of the flattened tubingand centered relative to the flattened tubing with opposite longitudinalmarginal portions of the flattened tubing extending beyond saidcylindrical portion,

each of said rotary means having portions on opposite sides of saidcylindrical portion overlying said marginal portions of the flattenedtubing, said overlying portions of the rotary means being reducedportions of less diameter than said central cylindrical portion topermit said marginal portions of the tubing to bulge away from theconcave surface towards the rotary means,

said rotary means having two opposite side portions overhanging theouter sides of said longitudinal marginal portions of the flattenedtubing to keep the flattened tubing centered relative to the rotarymeans.

3. A combination as set forth in claim 2 in which said rotary meanscomprises a roller of greater axial dimension than the width of theattened tubing,

said roller having two circumferential grooves positioned to registerrespectively with said longitudinal marginal portions of the flattenedtubing.

4. A combination as set forth in claim 2 in which the rotary meanscomprises a central roller of less width than the flattened tube and tworadial flanges rotatable with said roller and spaced from the oppositeends respectively of the roller to clear said longitudinal marginalportions of the tubing,

said flanges being of greater diameter than the central roller andstraddling the attened tubing to keep the flattened tubing centralizedrelative to the central roller.

5. A combination as set forth in claim 4 in which the two opposite endsof said central roller are rounded in prole.

References Cited UNITED STATES PATENTS 3,402,673 9/1968 Ballentine etal. 103-149 3,122,103 2/1964 Ormsby 103-149 2,434,802 1/1948 Jacobs103-149 1,765,360 6/1930 Baumann 103-149 2,987,004 6/1961 Murray 103-149FOREIGN PATENTS 1,380,460 10/1964 France 103-149 851,331 1/1959 GreatBritain 103-149 HENRY F. RADUAZO, Primary Examiner

